The predecessor in interest of the assignee of this Application invented and developed the first self-piercing female fastener, now commonly referred to as a pierce nut as shown, for example, in U.S. Pat. No. 2,707,322. The pierce nut disclosed in this patent has been commercially successful, particularly for mass production applications for attachment of one component to a second component by the automotive and appliance industries. In a typical application, the pierce nut is installed in a metal panel by an installation head, which is commonly installed in the upper die shoe or platen of a die press, and a die member or die button is installed in the lower die shoe or die platen. The pierce nuts are fed to the installation head, which includes a reciprocating plunger, and a pierce nut is installed by the plunger with each stroke of the die press. The panel to which the pierce nut is installed may be simultaneously formed by the die press. Of course, numerous improvements have been made to the pierce nut disclosed in the above-referenced patent, including improved retention, by providing dovetail-shaped grooves on opposed sides of the pilot portion as described, for example, in U.S. Pat. No. 3,648,747, also assigned to the predecessor in interest of the assignee of the present application. Finally, in many mass production applications, it is preferable to assemble the pierce nuts in a continuous frangible strip, as disclosed in U.S. Pat. No. 3,845,860, which is also assigned to the predecessor in interest of the assignee of the present Application.
The pierce nuts disclosed in the above-referenced U.S. patents are formed by rolling the desired cross-sectional configuration of the pierce nut, generally starting with round wire, as known by those skilled in this art. The round wire is then rolled by flattening opposed sides of the wire and the wire is then continuously rolled into the desired cross-section of the pierce nut, wherein the pierce nut section includes a rectangular central projecting pilot portion and flange portions on opposed sides of the pilot portion. In the Hi-Stress™ pierce nut, available from the assignee of this Application, grooves are rolled into the flange portion on opposed sides of the pilot portion preferably having at least one inclined groove wall, referred to as a “re-entrance” groove, which improves retention of the fastener on the panel following installation. The rectangular pilot portion of the pierce nut strip is then pierced, forming the pierce nut bore, and the section is then cut to length between the pierce bores and the bore may be tapped, if desired.
As will be understood by those skilled in this art and shown in the above-referenced U.S. patents, the pierce nuts formed by the rolling method described above are rectangular and include a rectangular pilot portion. However, in certain applications, it is desirable to have a pierce nut of the type described above, wherein the pilot portion is not rectangular, but is generally cylindrical for example. It has not been possible, however, to form a pierce nut having a generally cylindrical pilot portion by conventional rolling processes. It is an object of this invention to combine the advantages of a high speed rolling process with conventional cold header or progressive die techniques to form a pierce nut of the type described above having a pilot portion which is not rectangular and preferably generally cylindrical in shape.